Magnetic bubble memories are well known in the art. One mode of operating such memories is called a field access mode as is also well known. A field access mode bubble memory is characterized by a magnetic field reorienting, typically rotating, in the plane of bubble movement. Bubbles, in response to the cyclical changes in the magnetic field move along paths defined by magnetically soft elements such as permalloy or, more recently, by a repetitive pattern of ion-implanted regions.
The most attractive organization for a field access bubble memory is called the major-minor organization. This organization includes a plurality of closed-loop paths, termed minor loops, and a single major path or loop. A bubble generator and a bubble detector are associated with the major path in spaced-apart positions operative to produce a bubble pattern in the major path and to detect such a pattern respectively.
Movement in all the paths is produced by the rotating magnetic field. Bubble movements in the minor loops and the major path thus are synchronous. Accordingly, bubble movement between the minor loops and the major path is achieved by the generation of appropriate magnetic control fields during a selected cycle of the magnetic field.
Commonly, the control fields are generated at the ends of the minor loops where those loops come into close proximity with the major path. At those ends, the geometries of the ion-implanted regions, for example, are different and an electrical conductor is coupled to the layer of bubble movement at the positions of close proximity so that bubbles can be moved between the minor loops and the major path by a pulse on the conductor during a selected cycle.
Frequently, a separate conductor couples positions of close proximity between minor loops and the major path at each set of ends of the minor loops. The elements and conductors at one set of ends are adapted to transfer bubble patterns into the minor loops; those at the other set of ends being adapted to transfer bubble patterns out of the minor loops. It can be seen that bubbles from the generator are organized in the major path for transfer into the minor loops for permanent storage while bubbles permanently stored in the minor loops are transferred out to the major loop for detection all in response to the rotating magnetic field and appropriately timed transfer-in and transfer-out pulses.
Whatever the organization, a transfer port is important and, of course, optimization of operating margins of such a transfer is highly desirable also. For such optimization, it is helpful to bring as close together as possible the two paths between which transfer is to occur. But a rule-of-thumb in bubble memory design is that adjacent bubbles are to be spaced apart four to five bubble diameters. This constraint dictates typical spacings in bubble memory design. The problem thus is to achieve a functional bubble operation such as transfer between paths closer than the rule-of-thumb dictates.
The solution to this problem is based on the use of worse-case orientation for the merge port disclosed in copending application Ser. No. 99,556 filed for T. J. Nelson and R. Wolfe (Case 13-18).